The invention relates to a method and an apparatus for positioning sheet metal edges for butt welding.
When welding thin-walled tubes meaning tubes with a ratio of tube diameter to tube material thickness of, say, a 65 it is known from DE-C-4432674 to hold the tube with a clamping device involving the use of an inner support arm. Positioning the tube in this clamping device is relatively tricky and expensive. Meanwhile there is an increasing demand for welded thin-walled tubes in extremely diverse cross-sections which can subsequently be shaped into components e.g. for the motor vehicle industry e.g. by internal high pressure forming (hydroforming). The forming process depends on the presence of a weld seam of high quality, which in turn requires the abutting edges to be precisely located during welding. The same requirement also arises, of course, in the butt welding of flat sheet-metal items.
Hence one fundamental problem of the invention is to provide a method and/or an apparatus allowing the edges to be precisely positioned.
This problem is solved, in the case of a method of the kind by a method and apparatus for positioning sheet metal edges as they are moved to a welding point for welding by a laser. An endless locator projects between the edges and travels with the edges along a leg of a conveyor path leading to a welding point. The locator element is formed by a revolving chain or belt and has a plurality of stops. At least one endless forming element also travels with the edges toward the welding point for acting on the sheet margin. The forming element may be a chain or belt with a plurality of forming pieces preferably exchangeably arranged thereon.
By providing a locator element travelling with the edges to be welded, the edges can be positioned against this element with suitable force without any possibility of the positioning""s being compromised by friction forces between edges and locator element.
Preferably, the locator element is adapted to assist the bringing together of the edges by provided it with wedge-shaped stops projecting between the edges to different depths. A preferred application of the method lies in the welding of preformed rounds into tubes, particularly into thin-walled tubes. The exact positioning and bringing together of the edges that can be achieved is especially advantageous in this application.
A further problem of the invention is to provide an apparatus for positioning sheet-metal edges.
This is accomplished, in the case of the apparatus stated at the outset, in which the locator elements project between the edges of the sheet metal along the leg of the conveyor path.
The endless element moving with the edges provides a stop that allows frictionless contact to be made between the sheet-metal edges being conveyed, and hence allows precise positioning.
Preferably, the apparatus has wedge-shaped stops and moreover preferably has an adjustable carrier for the endless element enabling the latter""s point of insertion and depth of insertion to be adjusted.
According to the state of the art, rollers are used on the outside of the sheets: in particular, profiled rollers adapted to the outer contour of the tube are used near the welding zone to position the sheets, tube-round, or sheet edges. These rollers are positioning elements acting merely in line, and in the welding zone they have to be cooled, which is expensive.
Therefore the problem exists of providing a means of acting on the sheet to position the sheet, again with a particular view to obtaining the weld quality required for tubes, and thin-walled tubes in particular, especially when the tubes are to be subsequently subjected to internal high pressure forming. A similar problem of edge positioning can also arise in the welding of flat sheets.
The problem is solved, in the case of a method of the kind stated at the outset.
By subjecting the sheet to the action of an endless forming element which moves with the sheet along a leg of the conveyor path, regions of the sheets can be acted upon in a way that allows their edges to be very accurately positioned with respect to each other. Because the endless forming element travels past the welding point and does not remain stationary, special cooling for the said element is usually unnecessary.
The forming element is preferably provided as a cup-shaped containing element for the sheet, particularly in the upper part of a tube-round, and on either side of the weld line.
A further problem of the invention is to provide an edge-positioning apparatus which does not possess the above-mentioned disadvantages.
This is solved, in the case of an apparatus of the kind stated at the outset.
The endless forming element provides a continuous rest for the sheet margins, allowing precise positioning of the edges, even if the sheets are very thin. Furthermore, the forming element does not need cooling.
A further problem of the invention is to cater for the welding of tapered tubes, preferably by the above-mentioned methods. This is realized by arranging a conically preformed tube-round in a conical die and a weld side upper closure of the die has at least one endless forming element conveyed with the die.
A further problem of the invention is to provide an apparatus for welding tapered tubes, preferably corresponding to one of the above-mentioned apparatuses.
This problem is also solved by a conical die to contain the tube-round and at least one forming element that is conveyed with the die to a welding station.